Improved quench oil for high temperature coking of residua



IMPROVED QUENCH OIL FOR HIGH TEMPERA- TURE COKING F RESIDUA George F.Pappas, Westfield, N.J., assignor to Esso Research and EngineeringCompany, a corporation of Delaware Application December 3, 1956, SerialNo. 625,838

3 Claims. (Cl. 208- 102) This invention relates to an improved hightempera ture fluidized solids process for the coking of heavy oils. Itis particularly concerned with an improved method for quenching the hightemperature vapors obtained by coking of heavy oils.

In brief compass this invention is concerned with an improved fluidizedsolids, transfer line, heavy oil coking process for the production ofchemicals and chemical intermediates such as low molecular weightunsaturates and aromatics. The transfer line coking process comprisescontacting a heavy oil in a transfer line coking zone with flowingfluidized particulate solids maintained at a temperature above 1200 F.,to produce vaporous product and carbonaceous residue which is depositedon the particulate solids. The particulate solids are separated byconventional means, such as by cyclone, from the vaporous product.

The improvement of this invention is concerned With the quenching ofthis vaporous, high temperature product. This improvement comprisesinjecting into the vaporous product, after the solids are separated, aliquid quench medium obtained in a particular manner. This quenchingquickly lowers the temperature of the vapors below about 700 F., andforms a liquid-vapor mixture.

To obtain the liquid quench medium, this liquid-vapor mixture isseparated to obtain at least a naphtha product, a light gas oil fractionboiling in the range of 430 to 650 F., and a tar bottoms having aninitial boiling point immediately above the end boiling point of thelight gas oil fraction. The heavy tar bottoms is then stripped to obtainan overhead fraction having a final boiling point below about 800 F.This overhead fraction obtained by the stripping is condensed andcombined with a portion of the light gas oil fraction to obtain theliquid quench medium.

It is known to convert hydrocarbon oils, particularly heavy hydrocarbonoils such as residua, by contacting the oils with highly heatedfluidized particulate solids unidirectionally flowing in a narrowlyconfined, elongated, conversion chamber or transfer line conversionzone. In this process, solids having a temperature above about 1200 F.are flowed through a transfer line zone by means of a fluidizing gas,e.g., steam, at a density of about 5 to 50 lbs./ cu. ft. The oil to beconverted is injected into the flowing solids and, upon contact with thesolids, undergoes pyrolysis forming vaporous conversion products andcarbonaceous residue or coke which is deposited on the solids. After arelatively short contact time, i.e., usually 0.15 to 1.0 second beforequench, the solids are separated from the vaporous products thus formed,and the vaporous products are quickly cooled to arrest furtherconversion and avoid undesirable secondary reactions. The thus cooledvapors are then further separated as desired to recover the desiredproducts such as low molecular weight unsaturates, as ethylene andbutadiene, and aromatics.

Any suitable, relatively finely divided solid can be used tcs Patent2,901,418 Patented Aug. 25, 1959 ice in this process. The coke particlesproduced in the process can themselves be used. Materials such as metalparticles, ceramic beads, kieselguhr, and the like can also be used.These solids, along with the deposited coke, after being separated fromthe conversion products, are usually heated in some manner in anexternal heating zone. This can comprise a transfer line zone similar tothe transfer line conversion zone, or can be a fluid bed or gravitatingbed unit wherein the solids are contacted with a free oxygen-containinggas and burned to remove coke deposits and to raise their temperature 50to 400 above the conversion temperature. Indirect means can also be usedto heat the solids, or an extraneous gaseous, liquid or solid fuel canbe injected into the burning zone. After being so heated, the solids arerecycled to the reaction zone to supply the requisite heat for thepyrolysis.

In the previous coking designs, the vaporous reactor products arequenched normally by injecting a cool liquid directly into the vapors.The liquid used is preferably a hydrocarbon oil and can comprisematerial separated from the reactor products. In this arrangement,however, severe coking has been experienced at the quench point. Thereactor products contain an appreciable amount of tarry materials orcoke precursors. In being cooled from the high reaction temperature to arelatively cool temperature, these tarry materials have an opportunityto condense on surfaces at intermediate temperature near the quenchpoint, which temperature is still sufi'iciently high to allow furtherconversion; These tarry materials or coke precursors, when condensed,rapidly cause appre ciable coke deposits which can cause fouling orcomplete shutdown of theequipment.

A large quantity of liquid diluent in the line downstream from thequench point will dilute, and wash away coke and heavy condensationproducts. In previous designs, however, where a stream separated fromthe reaction products is recycled as the liquid quench medium, thereisnormally not enough material available to supply any large amount ofliquid wash at the quench point and beyond.

The present invention proposes an improved method for obtaining therequired quantity ofliquid diluent or quench medium from the reactionproducts to overcome this specific problem.

In the present invention, the products are separated in a conventionalmanner to obtain naphtha andlighter materials, a light gas-oil fractionand a heavier tar bottoms. In the past, the light gas oil fractionhaving a. boiling range of about 430650 F. would normally be used as theliquid quench medium. When this light gas oil fraction is so used,however, at the temperature of quenching, practically all of itvaporizes without leaving suficient liquid to wash away the cokedeposits, i.e., the amount of higher boiling material normally availablein the vaporous reaction products is not suflicient to supply thedesired quantity of wash liquid in the liquid quench medium.

This invention proposes that a narrow fraction, within a boiling rangeof about 650800 F., be separately removed from the reactor products andrecycled back to the quench point along with a portion of the liquid gasoil fraction, to provide the necessary washing actionand thus preventcoking. This narrow fouling diluent or liquid wash fraction is separatedby steam stripping the heavy tar bottoms, followed by condensationbefore it is returned to the quench point.

Stated somewhat dilferently, this invention proposes that two separatefractions be recovered from the vaporous reaction products from thecoking zone to permit both rapid cooling of the high temperaturevaporous products by vaporization of the liquid quench medium, and

washing of theheavy condensation-products fromtthe vaporous products.

In the specific manner of this invention, the separate recovery of'theliquid wash -component of-the quench fnedium ;permits-recirculationofenough of it to overcomethe problem of coking after quench or-beyondthe quench point. By the present method, the circulation ofthe liquidwash" diluent can be varied as required by the process. Thus, theproblem of-insufiicient production ofintermediate boiling range materialboilingat a temperature of about 650-;800 F. is satisfactorily overcome.i l

The following description of the drawingattached-to and forming a partof thisspecificationwil lserve, to make this invention clear. M A iIllustrated -is a transfer line chemicals coking apparatus for"thefconversion of heavy oils to chemicals and hemi: cal intermediates. Awide range offeed -ss1s;chi}be used in this process, "such asnaphthasjlight and heavy gas oils, residua or even whole crudes. Thisinvention is most applicable to heavy; oil ssuch as residua, shale oils,tars, as'phalts, coal tars and the likel that contain an appreciableproportioflof materialsinon yaporizable at atmospheric pressure withoutdegradation, i1e., contain more than of such materials. Thesel extremely heavy constituents in oils of this type account for the cokeprecursors or tarry materials in the i conversion products fromthe'coking zone. It is, therefore, with this-type of feed thatcQkingfOfthe quench point is most pronounced andfthus this invention 'ismost applicable to this type of feed. With lighterfeeds such aa naphthasand gasoils, the problem is not so severe.

Referring tothedrawing, there is shown atransferline coking zone 1, asolids recovery system or cyclone. 2, and an associated soaker or solidsreservoir chamber 3. A heavy oil, e.g. a, residuum, is injected .intothis transfer line 'zone l by line 341mm contacts thereinflowingxparticulatesolids 'maintainedat a temperature above 1200" F. Thedensity of the solids may range from 2 to lbs/cu. ftIThe solidspass;upithrough thetransfer line zone at a' velocity' above about 60ftQ/secl :Upon contact with the solids, the residuum; undergoes conversion depositing coke on the solids and evolving lighter vaporousconversion products. The conversion products are separatedfrom thesolids in cyclone'2.

This cyclone 'dilfers somewhat .fromthe standard cyclones. In-theconventional cyclones, an internal outlet pipe or duct extends down intothe cyclone barrel and. is eiipo'sed to'the gas strambothinside andoutside. For operation above the softeningtemperature ,of structuralmetals,' which in this case maybe ashigh as '2000 F., this" outlet pipemust be internally cooled or alternatively made of unsupportedrefractory.material. In thepresent' c'a'seI'the top 'ofthe cyclone 'ismade in the shape of a truncated cone taper down) .as shown. in thedrawing. Thebasic cyclone flow pattern is retained but the outlet pipeis. eliminated, allowing the entire cycloneto bemade ofsupportedrefractory material. Thus the problern of erosion and weakeningof the outlet duct is avoided.

The vaporous products separated iri the cycloneare recovered overheadfrom the outlet duct byline 4. The separated solids pass downwardlythrough dipleg Sto. the

soakingfzone li' The separated solidsucontainsome re-..

sidual tarry andtaeky material. .Thefsolids are, therefore, retainedinthe soaking zone, to complete the conversion.,'of this;,material .and,.to strip outfthe. vapors. Solidsfare.mairitaimed in isoakingzone -isin a fluidized cond' llo n, inarnanher well knownin theart T o do this,steam or other suitable fluidiz-ing and stripping gas is. supplied tqlqb'rwfi of; zone 3-.by. line ,6. The secondaryconversion products forrneiin thesoaking. zone. are. removed overhead by .line; .7 and may. befurther: treated. as desired. Ifrdesired, .a.portion.of.the solids: fromthe soaking zone canpbe.,reciroulatedtto the. inlet:of-the transferlineZQIle 4 byline 8, although this is not mandatory. Another portion ofthe solids in the soaking zone is transferred by line 9 to an externalheating zone, not shown, as previously described. Heated solids arereturned from the heating zone by line 10 to the inlet of the transferline zone. The solids are conveyed in these lines by aeration orconveying gas such as steam, inert gases, and the like in a manner knownin the art.

The solids injected in the base of the transfer line zone are picked upbya suitable conveying gas, such as steam, nitrogen orlighthydrocarbons, supplied by line 11. The amount of gas used is sufficientto give the required velocity, in. the. transfer line zone, density ofsolids, and hydrocarbon vapor partial pressure. When steam is used, theamount of steam may vary from 0.01 to 0.05 lb./ lb. of fresh feed.

The apparatus so far described illustrates one form of transfer linecoking of residual oils to produce chemicals andforms no particular partof'the present invention. Other forms ofcoking will occur to those;skilled in the art.

The present invention is concerned with the treatment or quenching ofthe high temperature vaporousproducts in line 4; After emerging fromcyclone 2; the products are immediately quenched by a liquid: quenchmedium supplied to line 4 by line 12; The temperature and amountof thisliquid quench medium is sufficient'to cool the vapors below 700" R,preferably below 600 F. 'In normal operations, the vapors arequenchedinthis manner within-0.l5 to 1.0 sec. from the time of feed injection'intoreactor. The'quench material is transferred byline 15toscrubber-fractionator 14;

In the scrubber-fractionator, the quench vapors" are met with a recycledscrubbing oilsupplied by line 15. Condensed-materialpasses down into asettling zone 16 wherein. coke particles, notremoved by cyclone 2, areallowed to settle out from the tar bottoms. A slurry-of these cokeparticles is withdrawn by line17-and canbe disposed-of as desired. Thisslurry may be recycled'to the transfer line coking zone.

There is condensed from the vapors passing up throughthescrubber-fractionator, a light gas oil product which is withdrawn -byline 13. Therem'ainder' of the vapors, comprising naphtha and lightermaterial, is withdrawn overheadby line 19-and-may-be further treated asdesired; such as by distillation, --fractionation, settling,crystallization, absorption and adsorption. The'separatecllight' gas oilproduct is collected in a surge drum 2% and "the product is withdrawn byline 21.- A portion of the lightgas oil is recirculated to the quenchpoint byline According to this invention, an addition to the light gasoilywhich is recycled as a quench medium, thetar bottoms collected inzone 16 have stripped therefrom'an intermediate boiling range fractionwhich will remain liquid-at the temperature resulting after quenching.To do this, the=temperature of theseparationis carefully controlled. Thetemperatures .of the various liquid frac-- tions given herein refer tothe flash'vaporization-temperature.

Thus,- according tothis'invention; the light-gas oil product hasaninitial boiling point of about 430 "F. and a final lboiling point' ofabout 650- F. The1tarbottoms have:.an--I.B.P.:.of. about 650. Randinclude all material heavierv than. thelight .gas ,oil product. The.tarnbottoms are withdrawn, from Zone 16 lbyline 23 'via pumpv35.Aportion of .thebottoms are recycled. by line 15 as. the previouslydescribed scrubbing oil. The remainderof thewithdrawn tarbottoms. ispassed by line 24.through a heater 25 an'dthen is injected by line 26.into a stripper 27. The stripper. is supplied with a suitable strippingmedium, inthis case, steam, by line .28. There is recovered overheadfrom the stripper, an intermediate boiling range fraction having anI.B.P. contiguous to thatof the light gas oilproduct; an'da-finalboiling point below 800 'F.,

preferably below 700 F. This intermediate fraction recovered by line 29is condensed in condenser 30 and mixed by line 31 with the contents ofline 22. The combined mixture is passed to a pump 32, which recirculatesthe quench medium through line 12 to the quench point.

The remainder of the tar product is withdrawn from stripping zone 27 byline 33. It can be Withdrawn as product or can be recycled to thetransfer line conversion zone 1, to be further converted.

Example The feed stock comprises an 1100" F. I.B.P. South Louisianaresiduum, having a Conradson carbon of 17 Wt. percent, a sulfur contentof 0.74 wt. percent, a gravity of 107 API, and amounting to 2.4 wt.percent of crude. The average coking temperature in transfer line zone 1is 1400 F. The average residence time before quench is 0.75 sec. Thepressure at the cyclone outlet is 8 p.s.i. 5 wt. percent total steam onfresh feed is used to convey the solids to the transfer line zone. The Cconversion of the feed is 30 wt. percent based on fresh feed. Thetemperature of the vapors after quench is 500 F. The ratio of liquid tovapor after the quench is 1.0 1b./lb.

The quenched vapors are separated to obtain 26.8 wt. percent on freshfeed of 430 F. minus naphtha and lighter products, a 430 to 650 F. lightgas oil fraction and a heavy tar bottoms boiling immediately above this.20 wt. percent of this tar bottoms is recycled is a slurry to returnentrained solids. The remainder of the tar bottoms is stripped withsteam to remove a 650 to 700 F. intermediate boiling range fraction. 230wt. percent on fresh feed of the light gas oil fraction is combined withthis intermediate boiling range fraction, which amounts to 45.0 wt.percent on fresh feed, and the combined mixture is recycled to thequench point at a temperature of 240 F. as a liquid quench medium. There mainder of the light gas oil fraction, amounting to 7.6 wt. percenton fresh feed, and of the stripped tar bottoms amounting to 30 wt.percent on fresh feed, are withdrawn as products.

Having described this invention, what is sought to be protected byLetters Patent is succinctly set forth in the following claims.

What is claimed is:

1. In a process wherein hydrocarbon vapors having a temperature above1200 F. are produced and the vapors are quenched with a liquid quenchmedium, the

improved method of providing a liquid quench medium which comprisesseparating the vapors after quenching to obtain at least a naphthaproduct, a light gas oil fraction boiling below about 650 F., and a tarbottoms having an I.B.P. above about 650 F. and which includessubstantially all quenched vapors heavier than said light gas oilfraction; stripping from said tar bottoms an overhead fraction having afinal boiling point below 800 F., and condensing and combining saidoverhead fraction with a portion of said light gas oil fraction toobtain said liquid quench medium.

2. An improved fluidized solids transfer line heavy oil coking processfor the production of chemicals and chemical intermediates whichcomprises contacting a heavy oil in a transfer line coking zone withflowing fluidized particulate solids maintained at a temperature above1200 F. to produce vaporous product and carbonaceous residue which isdeposited on said particulate solids, separating particulate solids fromsaid vaporous products, thereafter injecting a liquid quench mediumobtained as described below into said vaporous product to quickly lowerthe temperature thereof below at least 700 F. and form a liquid-vapormixture, separating said mixture to obtain at least a naphtha product, alight gas oil fraction boiling in the range of 430-650 F., and a tarbottoms having an initial boiling point immediately above said light gasoil fraction and including substantially all vaporous product boilingabove said light gas oil fraction, stripping said tar bottoms to obtainan overhead fraction having a final boiling point below 800 F. andcondensing and combining said overhead fraction with a portion of saidlight gas oil fraction, and returning the combined material as saidquench medium.

3. The process of claim 2 wherein the heavy oil comprises a heavyresidua containing at least 10% of constituents non-vaporizable atatmospheric pressure without degradation.

References Cited in the file of this patent UNITED STATES PATENTS2,608,527 Holland .Aug. 26, 1952 2,656,307 Findlay Oct. 20, 19532,698,672 Burnside et a1 Jan. 4, 1955 2,768,127 Kimberlin et a1. Oct 23,1956 2,776,727 Boisture Jan. 8, 1957 2,776,931 Chaney et a1 Jan. 8, 19572,847,356 Beuther et a1 Aug. 12, 1958

2. AN IMPROVED FLUIDIZED SOLIDS TRANSFER LINE HEAVY OIL COKING PROCESSFOR THE PRODUCTION OF CHEMICAL AND CHEMICAL INTERMEDIATES WHICHCOMPRISES CONTACTING A HEAVY OIL IN A TRANSFER LINE COKING ZONE WITHFLOWING FLUIDIZED PARTICULATE SOLIDS MAINTAINED AT A TEMPERATURE ABOVE1200* F. TO PRODUCE VAPOROUS PRODUCT AND CARBONACEOUS RESIDUE WHICH ISDEPOSITED ON SAID PARTICULATE SOLIDS, SEPERATING PARTICULATE SOLIDS FROMSAID VAPOROUS PRODUCTS, THEREAFTER INJECTING A LIQUID QUENCH MEDIUMOBTAINED AS DESCRIBED BELOW INTO SAID VAPOROUS PRODUCT TO QUICKLY LOWERTHE TEMPERATURE THEREOF BELOW AT LEAST 733*F. AND FORM A LIQUID-VAPORMIXTURE SEPARATING SAID MIXTURE TO OBTAIN AT LEAST A NAPHTHA PRODUCT ALIGHT GAS OIL FRACTION BOILING IN THE RANGE OF 430-650*F. AND A TARBOTTOMS HAVING AN INITIAL BOILING POINT IMMEDIATELY ABOVE SAID LIGHT GASOIL FRACTION AND INCLUDING SUBSTANTIALLY ALL VAPOROUS PRODUCT BOILINGABOVE SAID LIGHT GAS OIL FRACTION, STRIPPING SAID TAR BOTTOMS TO OBTAINAN OVERHEAD FRACTION HAVING A FINAL BOILING POINT BELOW 800*F. ANDCONDENSING AND COMBINING SAID OVERHEAD FRACTION WITH A PORTION OF SAIDLIGHT GAS OIL FRACTION AND RETURNING THE COMBINED MATERIAL AS SAIDQUENCH MEDIUM.